See-through display apparatus

ABSTRACT

A see-through display apparatus includes a display device, and an optical coupler configured to obtain a combined image by combining a first image from the display device with a second image from a path different from a path of the first image, and emit the obtained combined image. The optical coupler includes a first surface on which the first image is incident, a second surface on which the second image is incident, and an exit surface through which the combined image is emitted. A noise reduction prism is disposed between the display device and the optical coupler, and includes inclined surfaces configured to perform path conversion so that, among light of the first image, effective light of a predetermined angle range is incident on the optical coupler and noise light of a remaining angle range remaining from the predetermined angle range is not incident on the optical coupler.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Korean Patent Application No.10-2018-0124577, filed on Oct. 18, 2018, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein in itsentirety by reference.

BACKGROUND 1. Field

The disclosure relates to see-through display apparatuses.

2. Description of the Related Art

Head-mounted displays that provide virtual reality (VR) have currentlybeen commercially available and have been widely used in entertainmentbusinesses. Head-mounted displays have also been developed for use inmedicine, education, and other industrial applications.

An augmented reality (AR) display that is an advanced form of a VRdisplay is an imaging apparatus that combines the real world with VR andmay provide an interactive experience between the real world and VR. Theinteractive experience between the real world and VR is based on afunction of providing information about a real world environment in realtime, and perception of and interaction with the real world are furtherenhanced by overlaying a virtual object or information on the real worldenvironment.

In the AR display, image noise and foreground noise may reach a user'sfield of view, thereby reducing visibility.

SUMMARY

Provided are see-through display apparatuses having reduced noise.

Additional aspects will be set forth in part in the description thatfollows and, in part, will be apparent from the description, or may belearned by practice of the presented embodiments.

According to an aspect of an embodiment, a see-through display apparatusincludes a display device, and an optical coupler configured to obtain acombined image by combining a first image from the display device with asecond image from a path different from a path of the first image, andemit the obtained combined image. The optical coupler includes a firstsurface on which the first image is incident, a second surface on whichthe second image is incident, and an exit surface through which thecombined image is emitted. The see-through display apparatus furtherincludes a noise reduction prism disposed between the display device andthe optical coupler, and including a plurality of inclined surfacesconfigured to perform path conversion so that, among light of the firstimage, effective light of a predetermined angle range is incident on theoptical coupler and noise light of a remaining angle range remainingfrom the predetermined angle range is not incident on the opticalcoupler.

The noise reduction prism may include an incident surface on which thefirst image is incident, a first inclined surface inclined with respectto the incident surface, and a second inclined surface inclined withrespect to the first inclined surface, the second inclined surfacefacing the first surface of the optical coupler.

The first surface of the optical coupler may be parallel to the secondinclined surface of the noise reduction prism.

An air gap may be disposed between the second inclined surface of thenoise reduction prism and the first surface of the optical coupler sothat the second inclined surface acts as a total reflection surface.

An inclination angle of the first inclined surface with respect to theincident surface may be set so that the effective light is totallyreflected by the first inclined surface to the second inclined surfaceand a part of the noise light is transmitted through the first inclinedsurface.

An inclination angle of the second inclined surface with respect to thefirst inclined surface may be set so that the effective light istransmitted through the second inclined surface and is incident on thefirst surface of the optical coupler.

An inclination angle of the second inclined surface with respect to thefirst inclined surface may be set so that a part of the noise light thatis totally reflected by the first inclined surface is totally reflectedby the second inclined surface through the first inclined surface.

The second inclined surface may be connected to the incident surface.

An angle between the second inclined surface and the incident surfacemay be a right angle, and an angle between the first inclined surfaceand the incident surface may be different from an angle between thefirst inclined surface and the second inclined surface.

The noise reduction prism may further include a third inclined surfaceconnecting the second inclined surface to the incident surface.

The third inclined surface may be parallel to the first inclinedsurface.

The noise reduction prism may further include a third inclined surfaceconnecting the first inclined surface to the second inclined surface.

The third inclined surface may be parallel to the incident surface.

The noise reduction prism may be disposed so that the incident surfaceof the noise reduction prism and the exit surface of the optical couplerare on a same plane.

The noise reduction prism may be disposed so that the incident surfaceof the noise reduction prism and the second surface of the opticalcoupler are on a same plane.

An angle between the first surface and the second surface of the opticalcoupler may be an obtuse angle.

The optical coupler may include an optical waveguide including the firstsurface, the second surface, the exit surface, and a third surfaceopposite to the first surface, a beam splitter disposed in the opticalwaveguide and inclined with respect to the exit surface, and a concavemirror disposed adjacent to the third surface.

The beam splitter may include a half mirror.

The see-through display apparatus may further include a plurality ofpolarizers configured to prevent a part of light of the second imagethat is obliquely incident on the second surface from being emitted fromthe optical coupler.

The plurality of polarizers may include a first polarizer disposed onthe second surface, and a second polarizer disposed on the first surfaceand having a polarization axis perpendicular to a polarization axis ofthe first polarizer.

The see-through display apparatus may further include a quarter-waveplate disposed between the third surface and the concave mirror, and athird polarizer disposed on the exit surface and having a polarizationaxis parallel to the polarization axis of the first polarizer.

The see-through display apparatus may further include an ellipticallypolarizing plate disposed on one surface of the beam splitter.

The see-through display apparatus may be a wearable device.

According to an aspect of an embodiment, a see-through display apparatusincludes a display device, and an optical coupler configured to obtain acombined image by combining a first image from the display device alonga first path, with a second image from a second path different from thefirst path, and emit the obtained combined image. The optical couplerincludes a first surface on which the first image is incident, a secondsurface on which the second image is incident, and an exit surfacethrough which the combined image is emitted. The see-through displayapparatus further includes a noise reduction prism disposed between thedisplay device and the optical coupler, and including an incidentsurface on which the first image from the display device is incident, afirst inclined surface inclined with respect to the incident surface,and a second inclined surface inclined with respect to the firstinclined surface, the second inclined surface facing the first surfaceof the optical coupler. A first angle between the incident surface andthe first inclined surface, a second angle between the first inclinedsurface and the second inclined surface, and a third angle between thesecond inclined surface and the incident surface are set so that, amonglight of the first image, effective light of a predetermined angle rangeis incident on the optical coupler and noise light of a remaining anglerange remaining from the predetermined angle range is not incident onthe optical coupler.

The first angle the second angle and the third angle may be set furtherbased on a critical angle for total reflection that is determined by thepredetermined angle range of the effective light and a refractive indexof the noise reduction prism.

The display device, the incident surface and the exit surface may be ona same plane, and an end portion of the optical coupler may be cut sothat the display device is disposed between the incident surface and theexit surface.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of the embodiments, taken inconjunction with the accompanying drawings in which:

FIG. 1 is a conceptual diagram illustrating a configuration of asee-through display apparatus according to an embodiment;

FIG. 2 is a view illustrating an optical path along which noise lightreaches a field of view in a see-through display apparatus according toa comparative example;

FIG. 3 is a view illustrating a configuration and an optical arrangementof a see-through display apparatus according to an embodiment;

FIG. 4 is a detailed view illustrating, according to an incidence angle,an optical path of light incident on a noise reduction prism provided inthe see-through display apparatus of FIG. 3;

FIG. 5 is a view illustrating a configuration and an optical arrangementof a see-through display apparatus according to another embodiment;

FIG. 6 is a view illustrating a configuration and an optical arrangementof a see-through display apparatus according to another embodiment;

FIG. 7 is a view illustrating a configuration and an optical arrangementof a see-through display apparatus according to another embodiment;

FIG. 8 is a view illustrating a configuration and an optical arrangementof a see-through display apparatus according to another embodiment;

FIG. 9 is a view illustrating a configuration and an optical arrangementof a see-through display apparatus according to another embodiment;

FIG. 10 is a view illustrating a configuration and an opticalarrangement of a see-through display apparatus according to anotherembodiment;

FIG. 11 is a view illustrating a shape of a noise reduction prismemployed by a see-through display apparatus according to anotherembodiment along with an optical path according to various incidenceangles; and

FIG. 12 is a view illustrating a shape of a noise reduction prismemployed by a see-through display apparatus according to anotherembodiment.

DETAILED DESCRIPTION

The disclosure will now be described more fully with reference to theaccompanying drawings, in which embodiments are shown. The samereference numerals in the drawings denote the same elements, and sizesof elements in the drawings may be exaggerated for clarity andconvenience of explanation. Also, embodiments are described, and variousmodifications may be made from the embodiments.

For example, it will also be understood that when a layer is referred toas being “on” another layer, it may be directly on the other layer, orintervening layers may also be present therebetween.

As used herein, the singular forms “a,” “an,” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising” used herein specify the presence of statedcomponents, but do not preclude the presence or addition of one or moreother components.

The use of the terms “a” and “an,” and “the” and similar referents inthe context of describing the embodiments (especially in the context ofthe following claims) is to be construed to cover both the singular andthe plural.

Also, the steps of all methods described herein may be performed in anysuitable order unless otherwise indicated herein or otherwise clearlycontradicted by context. The disclosure is not limited to the describedorder of the steps. The use of any and all examples, or example language(e.g., “such as”) provided herein, is intended to better illuminate thedisclosure and does not pose a limitation on the scope of the disclosureunless otherwise claimed.

As used herein, the term “and/or” includes any and all combinations ofone or more of the associated listed items. Expressions such as “atleast one of,” when preceding a list of elements, modify the entire listof elements and do not modify the individual elements of the list.

FIG. 1 is a conceptual diagram illustrating a configuration of asee-through display apparatus according to an embodiment.

The see-through display apparatus according to an embodiment is adisplay apparatus that may combine a first image and a second image fromdifferent paths to obtain a combined image and may provide the combinedimage to an observer. The first image may be, for example, an imageformed by a display device and the second image may be a foregroundimage, that is, a real environment image.

The first image formed by the display device may include effective lightand noise light. Light of the first image undergoes reflection,refraction, focusing, etc. in an optical path through an optical coupleruntil reaching the observer's field of view. In this case, according toan emission angle of the light of the first image, part of the light ofthe first image that is reflected, refracted, and focused at a desiredposition and reaches the observer's field of view may be referred to aseffective light, and part of the light of the first image that isreflected, refracted, and focused at a non-desired position and thenreaches the observer's field of view to reduce image quality may bereferred to as noise light.

The see-through display apparatus according to an embodiment includes anoise eliminator at a side of the optical coupler on which light isincident to minimize noise. The noise eliminator performs pathconversion so that, from among light of the first image, only effectivelight is incident on the optical coupler and noise light is not incidenton the optical coupler, that is, is emitted to the outside of thesee-through display apparatus.

Accordingly, a combined image obtained by combining the light of thesecond image with the light of the first image that does not include thenoise light may be provided to the observer's field of view.

The first image may be a virtual reality (VR) image formed by thedisplay device to include additional information about the second imageof the real environment, and the see-through display apparatus of anembodiment may be applied to an augmented reality (AR) displayapparatus.

FIG. 2 is a view illustrating an optical path through which noise lightreaches a field of view in a see-through display apparatus 10 accordingto a comparative example.

The see-through display apparatus 10 according to the comparativeexample includes a display device 11, an optical waveguide 12, a beamsplitter 13, and a concave mirror 14.

The optical waveguide 12, the beam splitter 13, and the concave mirror14 collectively function as an optical coupler that combines light of afirst image from the display device 11 with light of a second image thatis an external image.

Upon examining an optical path along which light from the see-throughdisplay apparatus 10 reaches an observer's field of view, noise light Lnindicated by a dashed line, in addition to effective light Le indicatedby a solid line, reaches the observer's field of view.

A see-through display apparatus according to an embodiment employs astructure in which only the effective light Le from among image lightfrom a display device 100 may reach an optical coupler so that the noiselight Ln is prevented from reaching the observer's field of view.

FIG. 3 is a view illustrating a configuration and an optical arrangementof a see-through display apparatus 1000 according to an embodiment. FIG.4 is a detailed view illustrating, according to an incidence angle, anoptical path of light incident on a noise reduction prism 200 providedin the see-through display apparatus 1000 of FIG. 3.

The see-through display apparatus 1000 includes the display device 100,an optical coupler 700 configured to combine first light L1 of a firstimage formed by the display device 100 with second light L2 of a secondimage from a path different from a path of the first image, and thenoise reduction prism 200 located between the display device 100 and theoptical coupler 700 and configured to perform path conversion so thatnoise light L1_n from among the first light L1 is not incident on theoptical coupler 700.

The display device 100 forms the first light L1 of the first image bymodulating light according to first image information. The first imagemay be a two-dimensional (2D) image or a three-dimensional (3D) image,and examples of the 3D image may include a holographic image, astereoscopic image, a light field image, and an integral photography(IP) image, and may include a multi-view image or a super multi-viewimage.

Examples of the display device 100 may include a liquid crystal onsilicon (LCoS) device, a liquid crystal display (LCD) device, an organiclight-emitting diode (OLED) display device, or a digital micromirrordevice (DMD), and may include a next-generation display device such as amicro-LED device, a quantum dot (QD) display device, or an LED device.

The optical coupler 700 for combining the first light L1 of the firstimage with the second light L2 of the second image and emitting acombined image includes a first surface 300 a on which the first imageis incident, a second surface 300 b on which the second image isincident, and an exit surface 300 c through which the combined image isemitted.

The optical coupler 700 includes an optical waveguide 300 including thefirst surface 300 a, the second surface 300 b, the exit surface 300 c,and a third surface 300 d opposite to the first surface 300 a, a beamsplitter 400 located in the optical waveguide 300 and inclined withrespect to the exit surface 300 c, and a concave mirror 500 locatedadjacent to the third surface 300 d.

The beam splitter 400 may be a half mirror for reflecting part ofincident light and transmitting part of the incident light. However, thepresent embodiment is not limited thereto, and a polarization beamsplitter for reflecting one polarized light and transmitting anotherpolarized light may be used as the beam splitter 400.

The concave mirror 500 includes a concave reflective surface so that thefirst light L1 passes through the concave mirror 500 and the beamsplitter 400 and then is focused on an observer's field of view.

The noise reduction prism 200 includes a plurality of inclined surfacesthat change an optical path so that, from among the first light L1 ofthe first image, effective light L1_e of a predetermined angle range isincident on the optical coupler 700 and the noise light L1_n of aremaining angle range is not incident on the optical coupler 700.

Referring to FIG. 4, the noise reduction prism 200 includes an incidentsurface 200 a on which the first image is incident, a first inclinedsurface 200 b inclined with respect to the incident surface 200 a, and asecond inclined surface 200 c inclined with respect to the firstinclined surface 200 b and facing the first surface 300 a of the opticalcoupler 700.

The first surface 300 a of the optical coupler 700 and the secondinclined surface 200 c of the noise reduction prism 200 may be parallelto each other.

An air gap G may be formed between the second inclined surface 200 c ofthe noise reduction prism 200 and the first surface 300 a of the opticalcoupler 700 so that the second inclined surface 200 c acts as a totalreflection surface. However, the present embodiment is not limitedthereto and, for example, a material having a refractive index lowerthan a refractive index of the noise reduction prism 200 may be filledin the air gap G.

Inclination angles of the first inclined surface 200 b and the secondinclined surface 200 c may be determined so that the effective lightL1_e is incident on the first surface 300 a of the optical coupler 700and the noise light L1_n escapes from the see-through display apparatus1000 without being incident on the first surface 300 a of the opticalcoupler 700.

Upon examining a path of the effective light L1_e, the effective lightL1_e may be totally reflected by the first inclined surface 200 b to thesecond inclined surface 200 c, may pass through the second inclinedsurface 200 c without being totally reflected by the second inclinedsurface 200 c, and may be incident on the first surface 300 a of theoptical coupler 700.

Upon examining a path of the noise light L1_n, the noise light L1_n maybe transmitted through the first inclined surface 200 b, or may betotally reflected by the first inclined surface 200 b to the secondinclined surface 200 c and then may be totally reflected by the secondinclined surface 200 c.

Angles of the first inclined surface 200 b and the second inclinedsurface 200 c may be determined so that such optical paths are formedfor the effective light L1_e of the predetermined angle range and thenoise light L1_n of the remaining range.

An inclination angle of the first inclined surface 200 b with respect tothe incident surface 200 a may be determined so that the effective lightL1_e is totally reflected by the first inclined surface 200 b and atleast part of the noise light L1_n is transmitted through the firstinclined surface 200 b to the outside.

An inclination angle of the second inclined surface 200 c with respectto the first inclined surface 200 b may be determined so that theeffective light L1_e is transmitted through the second inclined surface200 c and is incident on the first surface 300 a of the optical coupler700 and the noise light L1_n totally reflected by the first inclinedsurface 200 b and incident on the second inclined surface 200 c istotally reflected by the second inclined surface 200 c.

Such angles are determined by also considering a critical angle fortotal reflection determined by an angle range of the effective lightL1_e and a refractive index of the noise reduction prism 200.

As shown in FIG. 4, the noise reduction prism 200 may have, but is notlimited to, a triangular prism shape in which the second inclinedsurface 200 c and the incident surface 200 a are connected to eachother.

A shape of the noise reduction prism 200 may be determined by alsoconsidering an arrangement of the optical coupler 700 and the displaydevice 100 in addition to the above requirements. For example, therequirements may be satisfied by causing an angle between the secondinclined surface 200 c and the incident surface 200 a to be a rightangle (90°) and causing an angle between the first inclined surface 200b and the incident surface 200 a and an angle between the first inclinedsurface 200 b and the second inclined surface 200 c to be different fromeach other. However, the present embodiment is not limited thereto, andthe requirements may also be satisfied even when the two angles are thesame according to an angle range of the effective light L1_e and arefractive index of the noise reduction prism 200.

FIG. 5 is a view illustrating a configuration and an optical arrangementof a see-through display apparatus 1001 according to another embodiment.

The see-through display apparatus 1001 includes the display device 100,the optical coupler 700 configured to combine the first light L1 of thefirst image formed by the display device 100 with the second light L2 ofthe second image from a path different from a path of the first image,and the noise reduction prism 200 located between the display device 100and the optical coupler 700 and configured to perform path conversion sothat, from among the first light L1, the noise light L1_n is notincident on the optical coupler 700 and the effective light L1_e isincident on the optical coupler 700.

The see-through display apparatus 1001 of the preset embodiment issubstantially the same as the see-through display apparatus 1000 of FIG.3 except for an arrangement of the display device 100 and the noisereduction prism 200.

While the noise reduction prism 200 is located so that the incidentsurface 200 a of the noise reduction prism 200 and the second surface300 b of the optical coupler 700 are on the same plane in thesee-through display apparatus 1000 of FIG. 3, the noise reduction prism200 is located so that the incident surface 200 a of the noise reductionprism 200 and the exit surface 300 c of the optical coupler 700 are onthe same plane in the see-through display apparatus 1001 of the presentembodiment.

FIG. 6 is a view illustrating a configuration and an optical arrangementof a see-through display apparatus 1002 according to another embodiment.

The see-through display apparatus 1002 includes the display device 100,the optical coupler 700 configured to combine the first light L1 of thefirst image formed by the display device 100 with the second light L2 ofthe second image from a path different from a path of the first image,and a noise reduction prism 202 located between the display device 100and the optical coupler 700 and configured to perform path conversion sothat, from among the first light L1, the noise light L1_n is notincident on the optical coupler 700 and the effective light L1_e isincident on the optical coupler 700.

The see-through display apparatus 1002 of the present embodiment issubstantially the same as the see-through display apparatus 1000 of FIG.3 except for a position of the display device 100 and a shape of thenoise reduction prism 202.

The noise reduction prism 202 includes an incident surface 202 a onwhich the first image is incident, a first inclined surface 202 binclined with respect to the incident surface 202 a, a second inclinedsurface 202 c inclined with respect to the first inclined surface 202 band facing the first surface 300 a of the optical coupler 700, and athird inclined surface 202 d connecting the incident surface 202 a tothe second inclined surface 202 c.

The noise reduction prism 202 may have a shape in which two triangularprisms having the same shape are connected to each other so that thethird inclined surface 202 d is parallel to the first inclined surface202 b.

From among light from the display device 100, the noise light L1_n maybe transmitted through the first inclined surface 202 b, or may betotally reflected by the first inclined surface 202 b and then may betotally reflected by the second inclined surface 202 c to escape fromthe see-through display apparatus 1002 without being incident on theoptical coupler 700, and the effective light L1_e may be transmittedthrough the first inclined surface 202 b and the third inclined surface202 d to the optical coupler 700.

FIG. 7 is a view illustrating a configuration and an optical arrangementof a see-through display apparatus 1003 according to another embodiment.

The see-through display apparatus 1003 includes the display device 100,an optical coupler 703 configured to combine the first light L1 of thefirst image formed by the display device 100 with the second light L2 ofthe second image from a path different from a path of the first image,and a noise reduction prism 203 located between the display device 100and the optical coupler 703 and configured to perform path conversion sothat, from among the first light L1, the noise light L1_n is notincident on the optical coupler 703 and the effective light L1_e isincident on the optical coupler 703.

The see-through display apparatus 1003 is substantially the same as thesee-through display apparatus 1001 of FIG. 5 except that the noisereduction prism 203 (including inclined surfaces 203 b and 203 c) and anoptical wave guide 303 of the optical coupler 703 is formed such thatend portions of the noise reduction prism 200 and an optical waveguide300 (including a first surface 303 a, a second surface 303 b and a thirdsurface 303 d) are cut to reduce a thickness, that is, a horizontalwidth in FIG. 7.

An incident surface 203 a of the noise reduction prism 203 is shiftedtoward a traveling direction of the first light L1 when compared to thesee-through display apparatus 1001 of FIG. 5, and the display device 100is located between an exit surface 303 c of the optical coupler 703 andthe incident surface 203 a of the noise reduction prism 203. That is,the display device 100 is located on the same plane as the exit surface303 c of the optical coupler 703, and thus a horizontal width of thesee-through display apparatus 1003 is reduced to be less than that ofthe see-through display apparatus 1001 of FIG. 5.

FIG. 8 is a view illustrating a configuration and an optical arrangementof a see-through display apparatus 1004 according to another embodiment.

The see-through display apparatus 1004 includes the display device 100,an optical coupler 704 configured to combine the first light L1 of thefirst image formed by the display device 100 with the second light L2 ofthe second image from a path different from a path of the first image,and a noise reduction prism 204 located between the display device 100and the optical coupler 704 and configured to perform path conversion sothat, from among the first light L1, the noise light L1_n is notincident on the optical coupler 704 and the effective light L1_e isincident on the optical coupler 704.

The see-through display apparatus 1004 of the present embodiment issubstantially the same as the see-through display apparatus 1001 of FIG.5 except for a shape of the noise reduction prism 204 and a shape of anoptical waveguide 304.

The optical waveguide 304 includes a first surface 304 a on which thefirst light L1 is incident, a second surface 304 b on which the secondlight L2 is incident, an exit surface 304 c through which light of acombined image is emitted, and a third surface 304 d opposite to thefirst surface 304 a. An angle between the first surface 304 a and thesecond surface 304 b is an obtuse angle, that is, an angle greater than90°.

The noise reduction prism 204 includes an incident surface 204 a, afirst inclined surface 204 b, and a second inclined surface 204 c, andthe second inclined surface 204 c is parallel to the first surface 304 aof the optical coupler 704. Accordingly, an angle between the incidentsurface 204 a and the second inclined surface 204 c of the noisereduction prism 204 is the same obtuse angle as that between the firstsurface 304 a and the second surface 304 b of the optical coupler 704.Two remaining angles of the noise reduction prism 204 may be determinedso that the noise light L1_n escapes from the see-through displayapparatus 1004 and the effective light L1_e is incident on the firstsurface 304 a of the optical coupler 704.

Because the optical waveguide 304 is shaped so that an angle between thefirst surface 304 a and the second surface 304 b is an obtuse angle,noise light L2_n from among the second light L2 of the second image maynot reach an observer's field of view. As shown in FIG. 8, the noiselight L2_n obliquely incident on the optical coupler 704 may be totallyreflected by the first surface 304 a and may escape from the see-throughdisplay apparatus 1004 without reaching the observer's field of view.

FIG. 9 is a view illustrating a configuration and an optical arrangementof a see-through display apparatus 1005 according to another embodiment.

The see-through display apparatus 1005 includes the display device 100,the optical coupler 700 configured to combine the first light L1 of thefirst image formed by the display device 100 with the second light L2 ofthe second image from a path different from a path of the first image,and the noise reduction prism 200 located between the display device 100and the optical coupler 700 and configured to perform path conversion sothat, from among the first light L1, the noise light L1_n is notincident on the optical coupler 700 and the effective light L1_e isincident on the optical coupler 700.

The see-through display apparatus 1005 of the preset embodiment issubstantially the same as the see-through display apparatus 1001 of FIG.5 except that optical members are further provided so that noise lightL2_n1 and noise light L2_n2 from among the second light L2 of the secondimage do not reach an observer's field of view.

A first polarizer 810 is located on the second surface 300 b of theoptical waveguide 300 and a second polarizer 820 is located on the firstsurface 300 a of the optical waveguide 300. The first polarizer 810 andthe second polarizer 820 may have polarization axes that areperpendicular to each other. For example, the first polarizer 810 mayhave a polarization axis for transmitting light of a first polarization(↔) and the second polarizer 820 may have a polarization axis fortransmitting light of a second polarization (⊙).

The noise light L2_n1 does not reach the observer's field of view due tothe first and second polarizers 810 and 820. The noise light L2_n1passes through the first polarizer 810 to become the light of the firstpolarization (↔), is incident on the second polarizer 820 perpendicularto the first polarizer 810, and is not transmitted through the secondpolarizer 820.

Also, a quarter-wave plate 840 may be located on the third surface 300 dof the optical waveguide 300, and a third polarizer 830 may be locatedon the exit surface 300 c of the optical waveguide 300. The thirdpolarizer 830 may have the same polarization axis as that of the firstpolarizer 810. That is, the third polarizer 830 may have a polarizationaxis for transmitting light of the first polarization (↔).

The noise light L2_n2 does not reach the observer's field of view due tothe quarter-wave plate 840 and the third polarizer 830. The noise lightL2_n2 passes through the first polarizer 810 to become light of thefirst polarization (↔), is transmitted through the quarter-wave plate840 to become circularly polarized light, and is reflected by theconcave mirror 500 to become circularly polarized light in the oppositedirection. Next, the noise light L2_n2 passes through the quarter-waveplate 840 to become light of the second polarization (⊙) and is incidenton the third polarizer 830. Because the third polarizer 830 transmitsonly light of the first polarization (↔), the noise light L2_n2 of thesecond polarization (⊙) is absorbed by the third polarizer 830.

The see-through display apparatus 1005 constructed as described abovemay remove the noise light L2_n1 and the noise light L2_n2 of the secondlight L2 not to be incident on the observer's field of view and mayprevent part of the effective light L1_e from the display device 100from leaking outward when being reflected by the beam splitter 400.

As shown in FIG. 9, part of the effective light L1_e may be reflected bythe beam splitter 400 that is a half mirror. Because the effective lightL1_e passes through the second polarizer 820 and then is incident aslight of the second polarization (⊙) on the optical coupler 700, theeffective light L1_e is absorbed by the first polarizer 810 thattransmits light of the first polarization (↔). Accordingly, an imageformed by the display device 100 may be prevented from leaking outwardand being perceived undesirably by another person.

Although the first through third polarizers 810, 820, and 830 and thequarter-wave plate 840 are provided to remove the noise light L2_n1 andthe noise light L2_n2 in FIG. 9, this is an example. If necessary,optionally, only the first polarizer 810 and the second polarizer 820may be provided, or only the first polarizer 810, the quarter-wave plate840, and the third polarizer 830 may be provided.

FIG. 10 is a view illustrating a configuration and an opticalarrangement of a see-through display apparatus 1006 according to anotherembodiment.

The see-through display apparatus 1006 includes the display device 100,the optical coupler 700 configured to combine the first light L1 of thefirst image formed by the display device 100 with the second light L2 ofthe second image from a path different from a path of the first image,and the noise reduction prism 200 located between the display device 100and the optical coupler 700 and configured to perform path conversion sothat, from among the first light L1, the noise light L1_n is notincident on the optical coupler 700 and the effective light L1_e isincident on the optical coupler 700.

The see-through display apparatus 1006 of the present embodiment issubstantially the same as the see-through display apparatus 1001 of FIG.5 except that an elliptically polarizing plate 410 located on onesurface of the beam splitter 400 is further provided.

The elliptically polarizing plate 410 is located on a surface of thebeam splitter 400 facing the first surface 300 a from among two surfacesof the beam splitter 400 so that part of the effective light L1_e doesnot leak outward when being reflected by the beam splitter 400. Theeffective light L1_e incident through the first surface 300 a becomeselliptically polarized light due to the elliptically polarizing plate410 before reaching the beam splitter 400, and part of the effectivelight L1_2 that becomes the elliptically polarized light is reflected bythe beam splitter 400 to become elliptically polarized light in theopposite direction and is incident again on the elliptically polarizingplate 410. The part of the effective light L1_2 that becomes theelliptically polarized light in the opposite direction by beingreflected by the beam splitter 400 is absorbed by the ellipticallypolarizing plate 410 without being transmitted through the ellipticallypolarizing plate 410.

In this structure, an image formed by the display device 100 may beprevented from leaking outward and being perceived undesirably byanother person.

FIG. 11 is a view illustrating a shape of a noise reduction prism 210employed by a see-through display apparatus according to anotherembodiment along with an optical path according to various incidenceangles.

The noise reduction prism 210 includes an incident surface 210 a onwhich first-first light L1_1, first-second light L1_2, first-third lightL1_3 of the first image formed by a display device are incident, a firstinclined surface 210 b inclined with respect to the incident surface 210a, and a second inclined surface 210 c inclined with respect to thefirst inclined surface 210 b and facing an optical coupler.

An angle α between the incident surface 210 a and the first inclinedsurface 210 b, an angle r between the first inclined surface 210 b andthe second inclined surface 210 c, and an angle β between the incidentsurface 210 a and the second inclined surface 210 c may be determined toperform path conversion so that effective light is transmitted throughthe second inclined surface 210 c and is incident on the optical couplerand noise light travels in a different direction.

Because the angles α, β, and r depend on an angle range of the effectivelight, a method of setting the angles α, β, and r will be described withreference to optical paths of the first-first light L1_1, thefirst-second light L1_2, and the first-third light L1_3 respectivelyhaving incidence angles of θ1, θ2, and θ3.

When the first-first light L1_1 having the incidence angle of θ1 iswithin the angle range of the effective light, an incidence angle α-θ1on the first inclined surface 210 b at a position

has to be greater than a critical angle for total reflection θc. Whenthe first-first light L1_1 is within an angle range of noise light, theincidence angle α-θ1 may be set to a value equal to or less than thecritical angle for total reflection θc.

When the first-second light L1_2 having the incidence angle of θ2 iswithin the angle range of the effective light, an incidence angle α+θ2on the first inclined surface 210 b at a position

has to be greater than the critical angle for total reflection θc sothat the first-second light L1_2 is totally reflected by the firstinclined surface 210 b. When the first-second light L1_2 is within theangle range of the noise light, the incidence angle α+θ2 may be set to avalue equal to or less than the critical angle for total reflection θc.Even when the first-second light L1_2 is totally reflected by the firstinclined surface 210 b and reaches the second inclined surface 210 c,conditions for an incidence angle α+θ2-r on the second inclined surface210 c may be set according to whether the first-second light L1_2 is theeffective light or the noise light.

When the first-third light L1_3 having the incidence angle of θ3 iswithin the angle range of the effective light, an incidence angle 90°β+θ3 on the second inclined surface 210 c at a position

has to be greater than the critical angle for total reflection θc sothat the first-third light L1_3 is totally reflected by the secondinclined surface 210 c. When the first-third light L1_3 is within theangle range of the noise light, the incidence angle α+θ2 may be set to avalue equal to or less than the critical angle for total reflection θc.

The three angles α, β, and r may be determined by considering the aboverequirements. The three angles α, β, and r may have different values, ortwo angles of the three angles α, β, and r may have the same value.Also, one angle of the three angles α, β, and r may be previously set toan obtuse angle or a right angle by considering a positionalrelationship with other optical elements provided in the see-throughdisplay apparatus.

FIG. 12 is a view illustrating a shape of a noise reduction prism 210′employed by a see-through display apparatus according to anotherembodiment.

The noise reduction prism 210′ has a shape including a fourth inclinedsurface 210 d connecting the first inclined surface 210 b to the secondinclined surface 210 c by cutting an end of the noise reduction prism210 having the angles α, β, and r of FIG. 11. Relative inclinationangles of the incident surface 210 a, the first inclined surface 210 b,and the second inclined surface 210 c are the same as those in FIG. 11,and thus path conversion may be performed so that effective light istransmitted through the second inclined surface 210 c and noise lighttravels in a different direction. Also, because the noise reductionprism 210′ is formed by cutting a portion of the noise reduction prism210, a volume of the see-through display apparatus employing the noisereduction prism 210′ may be reduced.

Because any of the above see-through display apparatuses may show bothan image formed by a display device and an image of the real world to anobserver, the see-through display apparatus may be used to implementaugmented reality (AR).

The AR may further enhance perception of and interaction with the realworld by overlaying a virtual object or information on a real worldenvironment. For example, at the observer's position, additionalinformation about the real world environment may be formed by an imageforming unit and may be provided to the observer. An AR display may beapplied to a ubiquitous environment or an Internet of things (IoT)environment.

The image of the real world is not limited to a real environment, andmay be, for example, an image formed by another imaging device.Accordingly, the see-through display apparatus may be applied to amulti-image display apparatus showing two images.

The see-through display apparatus may be configured as a wearableapparatus. All or some of elements of the see-through display apparatusmay be configured as wearable elements.

For example, the see-through display apparatus may be applied to ahead-mounted display (HMD) apparatus. Also, the disclosure is notlimited thereto, and the see-through display apparatus may be applied toa glasses-type display apparatus or a goggle-type display apparatus.

The see-through display apparatus may interoperate with or may operateby being connected to other electronic devices such as smartphones. Forexample, a controller for driving the see-through display apparatus maybe provided in a smartphone. In addition, the see-through displayapparatus may be provided in a smartphone, and the smartphone itself maybe used as a see-through display apparatus.

The see-through display apparatus may provide a combined image having areduced noise component of an image formed by a display device.

The see-through display apparatus may additionally provide a combinedimage having a reduced noise component of real image light, and/or mayprevent an image formed by a display device from leaking outward.

Accordingly, the see-through display apparatus may provide an AR displayhaving high quality.

While one or more embodiments have been described with reference to thefigures, it will be understood by one of ordinary skill in the art thatvarious changes in form and details may be made therein withoutdeparting from the spirit and scope as defined by the following claims.

What is claimed is:
 1. A see-through display apparatus comprising: adisplay device; an optical coupler configured to: obtain a combinedimage by combining a first image from the display device with a secondimage from a path different from a path of the first image; and emit theobtained combined image, wherein the optical coupler comprises a firstsurface on which the first image is incident, a second surface on whichthe second image is incident, and an exit surface through which thecombined image is emitted; and a noise reduction prism disposed betweenthe display device and the optical coupler, and comprising a pluralityof inclined surfaces configured to perform path conversion so that,among light of the first image, effective light of a predetermined anglerange is incident on the optical coupler and noise light of a remainingangle range remaining from the predetermined angle range is not incidenton the optical coupler.
 2. The see-through display apparatus of claim 1,wherein the noise reduction prism comprises: an incident surface onwhich the first image is incident; a first inclined surface inclinedwith respect to the incident surface; and a second inclined surfaceinclined with respect to the first inclined surface, the second inclinedsurface facing the first surface of the optical coupler.
 3. Thesee-through display apparatus of claim 2, wherein the first surface ofthe optical coupler is parallel to the second inclined surface of thenoise reduction prism.
 4. The see-through display apparatus of claim 2,wherein an air gap is disposed between the second inclined surface ofthe noise reduction prism and the first surface of the optical couplerso that the second inclined surface acts as a total reflection surface.5. The see-through display apparatus of claim 2, wherein an inclinationangle of the first inclined surface with respect to the incident surfaceis set so that the effective light is totally reflected by the firstinclined surface to the second inclined surface and a part of the noiselight is transmitted through the first inclined surface.
 6. Thesee-through display apparatus of claim 2, wherein an inclination angleof the second inclined surface with respect to the first inclinedsurface is set so that the effective light is transmitted through thesecond inclined surface and is incident on the first surface of theoptical coupler.
 7. The see-through display apparatus of claim 2,wherein an inclination angle of the second inclined surface with respectto the first inclined surface is set so that a part of the noise lightthat is totally reflected by the first inclined surface is totallyreflected by the second inclined surface through the first inclinedsurface.
 8. The see-through display apparatus of claim 2, wherein thesecond inclined surface is connected to the incident surface.
 9. Thesee-through display apparatus of claim 8, wherein an angle between thesecond inclined surface and the incident surface is a right angle, andwherein an angle between the first inclined surface and the incidentsurface is different from an angle between the first inclined surfaceand the second inclined surface.
 10. The see-through display apparatusof claim 2, wherein the noise reduction prism further comprises a thirdinclined surface connecting the second inclined surface to the incidentsurface.
 11. The see-through display apparatus of claim 10, wherein thethird inclined surface is parallel to the first inclined surface. 12.The see-through display apparatus of claim 2, wherein the noisereduction prism further comprises a third inclined surface connectingthe first inclined surface to the second inclined surface.
 13. Thesee-through display apparatus of claim 12, wherein the third inclinedsurface is parallel to the incident surface.
 14. The see-through displayapparatus of claim 2, wherein the noise reduction prism is disposed sothat the incident surface of the noise reduction prism and the exitsurface of the optical coupler are on a same plane.
 15. The see-throughdisplay apparatus of claim 2, wherein the noise reduction prism isdisposed so that the incident surface of the noise reduction prism andthe second surface of the optical coupler are on a same plane.
 16. Thesee-through display apparatus of claim 1, wherein an angle between thefirst surface and the second surface of the optical coupler is an obtuseangle.
 17. The see-through display apparatus of claim 1, wherein theoptical coupler comprises: an optical waveguide comprising the firstsurface, the second surface, the exit surface, and a third surfaceopposite to the first surface; a beam splitter disposed in the opticalwaveguide and inclined with respect to the exit surface; and a concavemirror disposed adjacent to the third surface.
 18. The see-throughdisplay apparatus of claim 17, wherein the beam splitter comprises ahalf mirror.
 19. The see-through display apparatus of claim 17, furthercomprising a plurality of polarizers configured to prevent a part oflight of the second image that is obliquely incident on the secondsurface from being emitted from the optical coupler.
 20. The see-throughdisplay apparatus of claim 19, wherein the plurality of polarizerscomprise: a first polarizer disposed on the second surface; and a secondpolarizer disposed on the first surface and having a polarization axisperpendicular to a polarization axis of the first polarizer.
 21. Thesee-through display apparatus of claim 20, further comprising: aquarter-wave plate disposed between the third surface and the concavemirror; and a third polarizer disposed on the exit surface and having apolarization axis parallel to the polarization axis of the firstpolarizer.
 22. The see-through display apparatus of claim 17, furthercomprising an elliptically polarizing plate disposed on one surface ofthe beam splitter.
 23. The see-through display apparatus of claim 1,wherein the see-through display apparatus is a wearable device.
 24. Asee-through display apparatus comprising: a display device; an opticalcoupler configured to: obtain a combined image by combining a firstimage from the display device along a first path, with a second imagefrom a second path different from the first path; and emit the obtainedcombined image, wherein the optical coupler comprises a first surface onwhich the first image is incident, a second surface on which the secondimage is incident, and an exit surface through which the combined imageis emitted; and a noise reduction prism disposed between the displaydevice and the optical coupler, and comprising an incident surface onwhich the first image from the display device is incident, a firstinclined surface inclined with respect to the incident surface, and asecond inclined surface inclined with respect to the first inclinedsurface, the second inclined surface facing the first surface of theoptical coupler, wherein a first angle between the incident surface andthe first inclined surface, a second angle between the first inclinedsurface and the second inclined surface, and a third angle between thesecond inclined surface and the incident surface are set so that, amonglight of the first image, effective light of a predetermined angle rangeis incident on the optical coupler and noise light of a remaining anglerange remaining from the predetermined angle range is not incident onthe optical coupler.
 25. The see-through display apparatus of claim 24,wherein the first angle the second angle and the third angle are setfurther based on a critical angle for total reflection that isdetermined by the predetermined angle range of the effective light and arefractive index of the noise reduction prism.
 26. The see-throughdisplay apparatus of claim 24, wherein the display device, the incidentsurface and the exit surface are on a same plane, and wherein an endportion of the optical coupler is cut so that the display device isdisposed between the incident surface and the exit surface.